Effects of dimensionality and magnetic correlations on superconducting properties of MoCo thin films*

The ability to precisely control superconducting transition within a narrow range of temperatures is crucial for many applications in cryogenic detectors. One way of achieving this is by utilizing magnetic impurities in superconductors. We present a systematic study of the effect of Co dopant on superconducting Molybdenum thin films prepared by sputtering from alloyed targets over a broad range of impurity concentrations and film thicknesses. Electric and magnetic measurements show strong dependence of the critical temperature on Co concentration, as well as presence of Kondo effect that vanishes as the film thickness is reduced. In addition to the pair-breaking effect due to magnetic impurities, we also explore the trend of T_C reduction with decreasing film thickness, generally attributed to the reduction of the superconducting order parameter on the surfaces.